1. Field of the Invention
The present invention relates to extraction and separation methods and apparatus using a supercritical fluid, and, more particularly, to the improvement of the mechanism of separating the extracted component.
2. Description of the Related Art
A safe and inexpensive extraction method which is free from toxicity, harm and odor is demanded in the food, perfume, pharmaceutical and cosmetic industry fields, etc.
For example, fish oils contain about 10% of 5,8,11,14,17-eicosapentaenoic acid (hereinunder referred to as "EPA) having five double bonds or about 10% of 4,7,10,13,16,19-docosahexaenoic acid (hereinunder referred to as "DHA) having six double bonds as a fatty acid which constitutes triglyceride. An EPA methyl ester and a DHA methyl ester attract medical attention as a physiologically active substances which are effective as a remedy for arteriosclerosis and myocardial infarction.
Attempt has heretofore been made to concentrate and purify these methyl esters from methyl ester compounds of fish oils by fractional distillation, liquid chromatography or the like.
These methyl esters, however, have many double bonds in a molecule, so that they are susceptible to denaturation due to heat and oxygen.
Fractional distillation and liquid chromatography, which involve the step of heating and exposing the extract for a long time in the process of operation, produce a problem of denaturation.
As a technique of liquid chromatography, a method of separating and analyzing olefins, in particular, in the cis form by using a silica gel column coated with silver nitrate is known and a method of separating an EPA methyl ester or a DHA methyl ester by using this technique has been reported.
By this method, however, the substance being separated is apt to be denaturated by heat at the time of removing the organic solvent contained in the fraction.
As a countermeasure, extraction and separation by using a supercritical fluid of carbon dioxide, for example, which can be operated under comparatively mild conditions has recently gathered attraction in place of fractional distillation and liquid chromatography.
A substance takes a solid, liquid or gas phase by varying the temperature and the pressure at a temperature below a predetermined critical temperature, but when the temperature exceeds the critical temperature, the substance cannot take a liquid phase any more however high pressure is applied thereto. A fluid in this state is called a supercritical fluid and has its characteristic physical properties which are not observed in general gas and liquid.
For example, the density of a supercritical fluid is several hundred times as high as that of a gas, rather closer to that of a liquid, but the viscosity thereof is substantially equal to that of a gas. The diffusion coefficient thereof is about 1/100 of that of a gas and several hundred time as large as that of a liquid.
Consequently, it is suggested that use of a supercritical fluid accelerates the movement, distribution and other physicochemical process of a substance more than use of a liquid. That is, use of a supercritical fluid as an extraction solvent or a mobile phase solvent can achieve more efficient extraction.
The conventional extraction and separation method and apparatus using a supercritical fluid, however, is disadvantageous in that a high concentration ratio cannot be obtained with respect to the components such as an EPA methyl ester and a DHA methyl ester.